Burst-mode transimpedance amplifiers (B-TIA), intended for use in the optical line termination (OLT) of gigabit passive optical networks (GPON), are preferably compliant to the ITU-T G.984.2 standard.
Burst-mode TIA must handle the upstream burst-mode transmission with the property that the signals arriving at the OLT consist of a rapid sequence of bursts with widely varying amplitudes from burst to burst.
Furthermore, to support the ITU-T G.984.2 class B, class B+ and class C operation, a TIA must have a large dynamic range. This can be provided by introducing means to provide a variable gain. Gain switching can extend the dynamic range, i.e. the level difference between the weakest and the strongest bursts that can be received.
A major problem in the development of a TIA front-end for a GPON system is the fact that after each burst, a reset signal is needed to prepare the receiver circuitry for a next burst. Indeed, in a conventional burst-mode receiver the automatic gain control circuitry needs to be reset after each burst.
When the guard time between bursts can be shorter than the maximum number of consecutive identical digits in a burst, it is not possible to detect the guard time between bursts. In that case in classical B-TIA's a reset signal needs to be provided externally to the TIA.
Usually, such a reset signal needs at least one additional I/O pin. This makes it difficult to integrate a TIA for GPON applications into the industry standard 5-pins TO-can package. Indeed, to ensure sufficient high sensitivity for class B, class B+ or class C operation an avalanche photodiode is required. Then, the following pins are needed:                Positive supply voltage for the TIA        Bias voltage for the avalanche photodiode        Negative supply voltage for the TIA (gnd)        Positive phase of the differential output        Negative phase of the differential outputHence, all 5 pins have been used, and no pins are left to provide a reset signal. In case only a PIN photodiode is used, one pin less can be used for monitoring. However, if one wants an additional RSSI (Received Signal Strength Indication) pin, the same problem remains, i.e. additional pins are needed on the TO-can package.        
One may conclude that prior art transimpedance amplifiers (TIA), that require gain switching on a per-burst basis, hereafter also referred to as a burst-mode transimpedance amplifier or B-TIA, require at least one additional I/O pin to provide a reset signal to the automatic gain adjustment circuitry or any other adaptation circuitry which needs to be set for each burst. When the guard time between bursts can be shorter than the maximum number of consecutive identical digits in a burst, it is not possible to automatically detect the guard time between bursts. In that case prior-art variable-gain burst-mode transimpedance amplifiers require a reset signal to be provided externally, with the packaging problems as described before.